Pathogenic fungi cause disease in plants and animals. Fungal plant pathogens threaten the yield and quality of agricultural crops costing farmers millions of dollars annually. Further, some fungal plant pathogens produce mycotoxins that are toxic to animals including humans. Fungicides have been developed that control the growth of fungal plant pathogens including those that produce mycotoxins.
Pathogenic fungi cause disease in plants and animals. Fungal plant pathogens threaten the yield and quality of agricultural crops costing farmers millions of dollars annually. Further, some fungal plant pathogens produce mycotoxins that are toxic to animals including humans. Fungicides have been developed that control the growth of fungal plant pathogens including those that produce mycotoxins.
Protecting crops from fungal pathogens is essential for global food security. Fungicides play a critical role in maintaining a reliable and high quality food supply by protecting crops from fungal diseases. Over the last 200 years, disease control has been achieved mainly by the use of inorganic and synthetic fungicides. These fungicides have been very effective and relatively inexpensive in controlling plant diseases. The reliance on fungicides for crop protection also led to the development of wide-spread fungicide resistance in pathogen populations globally. Furthermore the wide-spread use of fungicides across most cropping systems and production acreage also created degrees of environmental disturbance and pollution.
Fungal pathogens remain one of the major risk factor to human welfare by exerting a continued and increasing threat to global food security. See, Savary et al., Crop losses due to diseases and their implications for global food production losses and food security, 2012 December, Food Security, 4(4), 519-537. Fungicides are a primary tool in controlling fungal pathogens globally. However, global effectiveness of fungicides is severely impacted by wide-spread resistance to fungicides across key fungal pathogens. The impact that fungicide resistance exerts on the global food supply is further compounded by the economic, environmental and regulatory complexities associated with the development and commercialization of new classes of fungicides that address existing resistance issues.
Fungicide resistance is a heritable change in the sensitivity of a pathogen population to the mode of action of fungicides, a change that could manifest itself either as a rapid failure of disease control or as a gradual loss of the efficacy of the compound over time. The most common mechanisms of fungicide resistance involves mutation(s) of the target site known as target site insensitivity. Mutation or alteration of the biochemical target site generally confirms resistance to multiple fungicides that share a common mode of action (cross-resistance). Furthermore, the mode of action of modern fungicides is generally highly target site specific, and thus, these compounds are at a high risk for pathogen resistance due to mutation events occurring at the target site. In addition to target site insensitivity, additional mechanisms of documented fungicide resistance include the development of alternative metabolic pathways, increased rate of detoxification of the active ingredient, and increased removal of the toxic substance via diverse physiological mechanisms.
Effective management of fungicide resistance therefore is essential for global crop production and food security. To be most effective, resistance management strategies aimed at combatting and/or delaying the development of fungicide resistance need to be integrated into a holistic program within the cropping system and employed on a regional basis to also address the rapid and long distance dispersal of many fungal pathogens.
A fundamental aspect of fungicide utilization under the broader framework of resistance management is the rotation of fungicides with different modes of action. The selection of the most appropriate rotational partner is a complex process underlined by regulatory, biochemical, and economic considerations. In general, fungicides with complex multi-site modes of action are considered to be good rotational partners because of the significantly lower probability for the pathogen population to carry multiple mechanisms of resistance. The reduced risk of resistance development against fungicides with complex multi-site mode of action is demonstrated by the continued efficacy of some of the oldest inorganic fungicides against plant pathogens, e.g., copper or lime sulfur-based fungicides. In addition to fungicides with multi-site mode of action, compounds acting via a physical mode of action also provide an important tool for the management of biochemically based mechanisms of fungicide resistance. These compounds act via a physical mode of action on the propagules of the disease organism, e.g., negatively impacting spore impingement, spore germination, and the dispersal of airborne propagules.
Additional strategies also include seasonal limitations on the number of applications, use of mixtures of fungicides with different modes of actions, maintaining the recommended dose range for the fungicide, the timing and method of application of the fungicide and the incorporation of non-chemical management tactics into the overall program. The primary tenet of resistance management is reduction of differential survival between resistant and susceptible genotypes by reducing the selection pressure exerted on the pathogen population by a particular fungicide.
Many fungicides have been developed to control these fungal plant diseases. Common fungicides include benzimidazoles, dicarboximides, demethylation inhibitors including imidazoles, piperazines, and triazoles, phenyl amides, anilinopyrimidines, quinone outside inhibitors including strobilurins, phenylpyrroles, aromatic hydrocarbons including chlorophenyls and triadiazoles, cinnamic acid, hydroxyanilide, phosphonate, dithiocarbamate, chloroalkythios and chloronitriles. However, these fungicides have limited efficacy. Further, many plant diseases have developed resistance to these fungicides.
In contrast, botanically-sourced active ingredients are generally readily biodegradable and significantly less harmful to the environment. Unlike conventional fungicides which are typically based on a single active ingredient, plant derived pesticides usually comprise of an array of chemical compounds which affect a wide range of physiological functions in the target organism. As a consequence, the probability of resistance development against botanically sourced products containing a mixtures of compounds is reduced.
Sabadilla oil is an effective naturally derived fungicide found in the tissues of many of the plants of the genus Schoenocaulon, commonly referred to as sabadilla. Sabadilla oil is the byproduct obtained during extraction of alkaloids from the Sabadilla plant. Sabadilla oil does not contain the alkaloids, veratridine and cevadine. The species with the longest history of use, and the most readily available, is Schoenocaulon officinale. The plant is indigenous to Central and South America.
Fungicides must be cost effective to warrant their use on crops. Thus, the ability to reduce the cost of these fungicides is paramount to their use. One method to reduce cost is mixing more than one fungicide into one composition prior to application to crops, thus reducing the cost of application. Further, the application of more than one fungicide helps reduce pesticide resistance.
Thus, there is a need in the art for pesticide mixtures that contain plant derived fungicides.